1. Field of the Invention
This invention relates; to portable computer systems and more particularly to low battery detection and indicator circuitry for portable computer systems. This invention further relates to power management units for portable computer systems.
2. Description of the Relevant Art
It is frequently desirable to warn the user of a portable computer system of a condition when the battery capacity is low. Accordingly, a variety of battery monitors and so-called "fuel gauges"have been developed that provide an external indicator of a low battery-capacity condition. These external indicators include both LED indicators: and visual displays incorporated on the computer screen. The battery monitors may indicate when the battery capacity, as inferred by the voltage across the battery, decreases below a certain threshold, or may indicate the capacity of the battery over a broad range of possible values.
In portable computer systems, if the battery capacity is diminished to a critical point, damage to the battery and other system components may occur. If the computer is powered-on, the user may receive the indication of the low battery condition in real time and may accordingly power-down the system to recharge the battery. If, on the other hand, the computer is in a powered-off state or in a power-conserving suspend state (during which, for example, the CPU clock signal and the system clock signal may be stopped), the user may be unaware of a low battery condition. Thus, if the user subsequently attempts to turn on the computer system or the system attempts to restart the CPU and system clock signals, the battery will be drained even further. This can damage the battery and other system components.